Fuel continue to be the largest operating expenditure for airlines and is expected to cost them an extra $40 billion this year. So, MIT's developing a new style of aircraft that could run on as little as 30 percent as today's 737's.

The D8 "double-bubble" configuration, currently being developed by a research team at MIT in conjunction with NASA, is designed to maximize fuel efficiency. It's dual-aisle design not only doubles the plane's capacity (and carries more passengers per weight of fuel), it also widens the fuselage, which increases the plane's lift and allows for a smaller, nearly under-swept wing design. The D8 also attaches its engines, not to the underside of its wings, but at the base of its tail. This minimizes drag by pumping the jet exhaust directly into the plane's wake. According to Aviation Week,

Mark Drela, the MIT professor who developed the TASOPT optimization tool used to design the D8, says the aerodynamic advantages come from the lifting fuselage, which shrinks the wing; the nose-up pitching moment from the upturned nose, which shrinks the horizontal tail; and reducing Mach number to 0.72 from 0.80, which allows a lighter, more-efficient low-sweep wing.

Of the whole 70-percent fuel savings, an astonishing 49 percent of it was derived solely from design changes, not the application of new airframe and engine materials. The plane's next testing phase will employ a 1/11th scale powered model. Proving successful, development will continue and the skies will be filled with Double Bubbles by 2035. Assuming we haven't run out of jet fuel by then. [MIT via Aviation Week via DVice